Electric incandescent lamp



June 1957 D. R. BUIIRGENER ETAL 2,795,722

' ELECTRIC INCANDESCENT LAMP m 9 T m SQ? v mi M%+ n fa e M.r v lw e n s h OL D b Filed Dec. 29, 1954 United States Patent ELECTRIC INCANDESCENT LAMP Donald R. Burgener, East Cleveland, and Lester Hertz, Euclid, Ohio, assignors to General Electric Company, a corporation of New York Application December 29, 1954, Serial No. 478,349

3 Claims. (Cl. 313--117) Our invention relates, in general, to electric incandescent lamps and more particularly to a two-filament incandescent lamp for selectively producing, in conjunction with an associated reflector, either a colored beam of light or an uncolored white beam of light.

It has been customary to provide farm tractors with an implement lamp assembly on the rear of the tractor for the purpose of flood lighting any towed implement and the work being done by such implements at night. Recently, a second separate lamp bulb provided with a red color cap has been incorporated in such implement lamp assembly, within the lamp housing thereof, to serve as a red tail light for the tractor whenever driving on the highway. Because the installation of a second lamp bulb, socket and color filter is rather expensive and results in a complicated lamp housing construction, it has been proposed to provide such implement lamp assemblies with a single twofilament incandescent lamp to replace the two separate lamps and the color filter and capable of providing, on selective energization of the two filaments, either a red colored beam of light to serve as a red tail light or an uncolored white beam of light serving as an implement light.

It is an object of our invention therefor to provide a two-filament incandescent lamp suitable for the abovementioned purpose which is capable of selectively producing, when mounted in a reflector, either a colored or a white beam of light and which produces a minimum dilution of the colored light by leakage of white light from the lamp.

Another object of our invention is to provide a mount structure for a two-filament lamp of the above character which is simple in construction and easy to manufacture.

Briefly stated, in accordance with the invention, a twofilament incandescent lamp is provided with a set of three lead-in wires extending into the bulb from the neck end thereof and with a pair of linear coil filaments disposed in the bulb transversely of and spaced along and approximately in a common plane including the bulb axis, a pair of the lead-in wires being disposed approximately in the plane of and being connected to the opposite ends of one of said filaments, and the third one of said leadin wires along with one of the said pair of lead-in wires being extended to a point adjacent the top end of the bulb where they are connected to the other one of the filaments, the third lead-in wire being provided for such purpose with an offset inner end portion disposed approximately in the plane of the filaments. According to a further aspect of the invention, the bowl or top end portion of the lamp bulb is colored to conceal the forward or innermost filament in the bulb, and a light-intercepting shield is provided between the two extended lead-in wires and between the two filaments, in a position closely adjacent the forwardmost filament, to intercept all the direct radiation from the forwardmost filament other than that passing through the colored end portion of the bulb, the shield for such purpose being made of larger diameter than the distance between the inner ends 2,795,722 Patented June 11, 1957 of the extended lead-in wires and being secured at one side to one of the extended lead-in wires and peripherally notched at the other side thereof so as to partially surround the other lead-in wire closely without'touching it, thereby to provide efiective shielding of the forwardmost filament at that side of the shield.

Further objects and advantages of our invention will appear from the following detailed description of a species thereof and from the accompanying drawing.

In the drawing, Fig. 1 is an elevation, partly in section, of an electric incandescent lamp comprising our inven-. tion mounted in position in the reflector and socket of an associated lamp housing.

Fig. 2 is a fragmentary perspective view on an enlarged scale of the mount structure of the lamp comprising our invention.

Fig. 3 is a front end view of the lamp mount shown in Fig. 2 and Fig. 4 is a fragmentary perspective view of a modified form of lamp mount according to our invention.

Referring to the drawings, the invention is there illustrate-d as applied to an electric incandescent lamp for mounting in a lamp unit such as the conventional implement lamp assembly customarily provided at the rear of farm tractors and the like. Such implement lamp assemblies generally comprise a concave (usually paraboloidal) metal reflector 1 provided with a lamp-receiving socket 2 at the apex thereof and a cover glass or lens (not shown) across the mouth opening of the reflector.

The incandescent lamp according to the invention comprises a sealed glass bulb 3 of miniature size, such as that commercially known as an RP 11 bulb, having a neck portion to which a conventional type lamp base 4, such as a double end contact bayonet pin base, is suitably secured as by conventional basing cement. The bowl or top end portion of the bulb 3 is suitably colored (preferably red for the particular service intended) down to a predetermined cut-off line 5 around the bulb located a short distance beyond the region of maximum diameter thereof, as shown. The coloring of the bulb end may be produced by a suitable, color coating 6 thereon, such as an enamel or silicate coating, preferably applied to the exterior surface of the bulb.

Sealed into the bulb 3 and extending thereinto from the neck end of the bulb and more or less axially thereof is a lamp mount 7 comprising a glass stem tube 8 having a press portion 9 through which are sealed at set of three lead-in wires 10, 11 and 12. Exteriorly of the bulb 3, the lead-in wires 10, 11 and 12 are connected to the terminal contacts of the lamp base 4, two of the lead-in wires (i. e. 10 and 12) being connected to the end contacts 13 and 14 of the base and the other or third lead-in wire 11 being connected to the metal shell or side contact 15 of the base.

From the stem press 9 the three lead-in wires 10, 11 and 12 extend into the bulb more or less in the direction of the axis thereof and in triangular relation to each other with two of the lead-in wires (i. e. wires 10 and 11) disposed approximately in an axial plane of the bulb 3 and the other or third lead-in wire 12 disposed to one side of the said axial plane and preferably more or less midway between the two lead-in wires 10 and 11. One of the pair of lead-in wires 10, 11 (i. e. lead-in wire 10) extends only a relatively short distance into the bulb from the stem press 9, while the other one of said pair of lead-in wires (i. e. lead-in wire 11) and the third leadin wire 12 are extended inwardly of the bulb to a region adjacent the colored tip end thereof.

Disposed within the bulb 3 in spaced relation along the axis thereof is a pair of concentrated filaments comprising a main or major filament 16 and a minor filament .17 each constituted of fine wire of a suitable refractory metal such as tungsten. Thetwo filaments 16 and 17 are preferably in the form of linear coils of tungsten wire, having approximately the same voltage rating, and the minor filament 17. is of somewhat lower candlepower rating'than the major filament. 16; Thus, the major filament 16 may be ofapproximately 6 volt 32 candlepower rating, for example, and the minor filament 17 ma be of 6v volt 15 candlepower rating. The major filament 16' is'disposed-in' the bulb at a location inwardly from the neck end thereof at most approximately abreast of the cut-off line of the color coating 6 on the bulb, and preferably 'a short distance back of the said color cut-ofi line 5 sufficient to assure reception by the reflector 1, out to the outer periphery thereof, of direct uncolored radiations from the major filament 16 passing through th'eclear or uncoated portion of the bulb. The minor filament 17 is disposed within the bulb at a location near the top end or tip thereof so as to be located within and concealed by the colored end portion 6 of the bulb.

In accordance with the invention, the two linear coil filaments 16 and 17 are disposed approximately in a common axial plane of the bulb and approximately in the plane of the pair of lead-in wires 10 and 11, with the axes. of the filament coils extending transversely of or normal'to the bulb axis. The major filament 16 is connected at its opposite ends to the short lead-in wire 10 and to the extended lead-in wire 11 while the minor filament 17 is connected at its ends to the inner ends of the two extendedlead-in wires 11 and 12. For this purpose, the extended lead-in wire 12 is offset at its inner end to provide an offset inner end portion 18 to which the minor filament 16 is connected.

Positioned in the bulb between the two filaments 16 and 17 and between the inner ends of the extended leadin wires 11 and 12, is a light-intercepting shield 19 which is arranged to intercept all the direct rearward radiation from the minor filament 17 within the solid angle defined by the cut-off line 5 of the color coating 6 on the bulb, thus confining the radiations from the minor filament essentially to the colored end portion of the bulb. The shield 19 is preferably inthe form of a shallow dish-shaped or spherically cupped sheet metal member of circular con figuration disposed transversely of the bulb axis between the two lead-in wires 11 and 12 and as close as practical to the minor filament 17, with its concave side facing the said filament. Thus, in the particular case illustrated, the shield 19 is positioned a distance of the order of inch behind the minor filament 17, measured along the bulb axis.

The shield 19 is rigidly secured at one side thereof,

as by welding for instance, to one of the extended lead-in wires (i. e. lead-in wire 11) and is spaced at its other side a sufficient distance from the other extended lead-in wire 12 so as not to come in contact therewith during the normal usage of the lamp, with resulting short circuiting of the minor filament 17. In order to afford effective interception of the rearward direct radiations from the minor filament 17 and prevent excessive leakage of light out the clear or-uncoated rear portion of the bulb 3 such as would cause objectionable dilution of the color of the red or other colored beam emanating from the colored top end of the bulb, the shield 19 is preferably made of a diameter greater than the effective length of the minor filament 17. To accommodate such a size shield between the extended lead-in wires 11 and 12, the shield is preferably provided with a straight or flatsided portion 20 at that side thereof which is secured to the lead-in wire 11, while the opposite side of the shield is peripherally notched, as indicated at 21, so as to partially surround the lead-in wire portion 18 closely but Without touching it.

Fig. 4 illustrates a modified form of mount construction according to the invention in which the shield 19 is provided with additional support means in the form of an insulating or'sup plementary support brace 22 which is fastened to the lead-in wire portion 18 and to the shield 19, adjacent that side thereof opposite to the side welded to thelead-in wire 11, to reduce the possibility of the filament 17 being short-circuited by the contact of the shield, during the usage of the lamp, with the lead-in wire portion 18 at the point where the latter is closely surrounded by the notched portion 21 of the shield. As shown, the insulating bridge or supplementary support brace 22 may comprise a short length of glass rod 23 having short support wires 24 and 25 embedded in its opposite ends and suitably secured, as by welding for instance, to the lead-in wire'portion 18 and to the shield 19 adjacent the side thereof opposite to that side which is welded to the lead-in wire 11. As an alternative, the contacting of the shield 19 with lead-in wire portion 18, with resulting short-circuiting of the filament 17, may be prevented by providing a small mass or bead of suitable insulating material, such as glass, fused or otherwise secured either to the notched portion 21 of the shield or to the lead-in wire portion 18 at the vicinity of the notch 21 of the shield, or fused to both the lead-in wire portion 18 and the notched portion 21 of the shield.

When in use, the lamp according to the invention is mounted in place in the socket 3 of an associated lamp unit with the major filament 16 of the lamp located approximately at the optical focus of the reflector. When the major filament 16 is then energized alone, the direct radiations therefrom passing out the clear or uncolored rear portion of the bulb 3 impinge against the reflector and are reflected thereby forwardly from the lamp unit as a white or uncolored beam of light suitable for illuminating any implements being towed by the tractor or other vehicle on which the lamp unit is mounted, as well as the work being done by such implement. When the minor filament 17 is energized alone, the direct radiations therefrom which would normally pass out the clear or uncolored portion of the bulb are intercepted by the shield 19 and are redirected thereby out the red colored front or top end portion of the bulb where they combine with the direct radiations from the filament 17 passing through the red colored front end of the bulb to produce a reddish hued beam of light of sufiicient coloration to satisfactorily serve as a tail light for the vehicle.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. An electric incandescent lamp comprising a sealed glass bulb'having a neck portion and having its bowl end portion colored to a predetermined cut-ofi line defining a plane transverse to the bulb axis, and a mount sealed into said bulb and comprising a set of three leadin'wires extending into the bulb from the neck end thereof, a pair of said lead-in wires lying approximately in an axial plane of said bulb, a main filament in said bulb connected across said pair of lead-in wires and disposed in the bulb at a location inwardly from the neck end thereof at most approximately abreast of the said color cut-off line thereon, one of said pair of lead-in wires and the third one of said lead-in wires being extended inwardly of the bulb beyond said filament, a minor filament disposed within and concealed by the said colored end portion of the bulb and connected at its ends across the inner ends of said extended lead-in wires, and an approximately circular light-intercepting shield disposed within the said colored end portion of the bulb between the said filaments and between the inner ends of said extended lead-in wires and having a larger diameter than the spacing between and completelyv spanning the inner ends of said extended lead-in wires so as to confine the radiations from said minor filament essentially to the said colored end portion of the bulb, said shield being rigidly secured to one of said extended lead-in wires and having a small notch in its periphery opposite and within which the other one of said extended lead-in wires is located to thereby space the shield therefrom and prevent contact therewith.

An electric incandescent lamp comprising a sealed glass bulb having a neck portion and having its bowl end portion colored to a predetermined cut-off line defining a plane transverse to the bulb axis, and a mount sealed into said bulb and comprising a set of three leadin wires extending into the bulb from the neck end thereof in triangularly disposed relation with a pair of said lead-in wires lying approximately in an axial plane of said bulb, one of said pair of lead-in wires and the third one of said lead-in wires being extended inwardly of the bulb to a region adjacent the said colored end thereof, major and minor linear coil filaments in said bulb disposed transversely of and approximately in the bulb axis and approximately in a common plane including the said pair of lead-in wires, said filaments being spaced apart along the bulb axis with the major filament located inwardly from the neck end of the bulb at a position just short of the said color cut-ofi line thereon and the minor filament located within and concealed by the said colored end portion of the bulb, said major filament being connected across the said pair of lead-in wires and said filament so as to confine the radiations therefrom essentially to the said colored end portion of the bulb, said shield being rigidly secured to one of said extended leadin wires and being spaced from the other one of said extended lead-in wires to prevent contact therewith.

and the other one of said filaments located within and I concealed by the said colored end portion of the bulb, said one filament being connected to a pair of said lead-in wires and the said other filament being connected to an extended third one of said lead-in wires and to an extended one of the said pair of lead-in wires, a thin metal light-intercepting shield disposed within the said colored end portion of the bulb between the said filaments and between the said extended lead-in wires and closely adjacent the said other filament to confine the radiations therefrom essentially to the said colored end portion of the bulb, said shield being welded at one side to one of said extended lead-in wires and being peripherally notched at its other side to partially surround the other one of said lead-in wires closely, and an insulative supplementary support brace secured to the other one of said extended lead-in wires and to said shield adjacent the notched side thereof to additionally support the shield in place and prevent contact thereof with said other extended lead-in wire.

References Cited in the file of this patent UNITED STATES PATENTS 

